Mallory unilite electronic ignitin distributor and msd flamethrower coil. Noticed today while messing with electrical stuff my coil gets super hot while sitting with the key on. Is there anything to stop this from happening? Or should I just remove the hot wire from the coil if I'm keeping the key on for a while? Ballast resistor? Finishing wiring of the car and testing things, otherwise I wouldn't have ot sitting long periods of time with key on.
Never had a Unilite but it seems it act's just like points when key is left on. Remove wire from coil while working and never leave key on during normal use if engine isn't running.
Turn the key to the ACC position if you Don't need the engine running. Sent from my SM-T350 using The H.A.M.B. mobile app
Yep. That's how ignitions always have worked. Run the engine or switch to ACC. or burn your points, or coil... ....or unplug the hot wire. Sent from my SM-G981V using The H.A.M.B. mobile app
Same problem with electronic ignition (pertronix). Wired my radio to work only with key on, listed to the radio all day in the garage (with engine off). Burned up the coil. Replaced coil and rewired radio so it works with key off. Sent from my iPhone using The H.A.M.B. mobile app
Well... Say it's a coil with a 1 ohm primary coil, fed by 12V. 12V @ 1 ohm gives 12A going through it, 12V*12A gives 144W. A small item producing 144W of heat without any cooling (such as moving air) will become quite hot.
I did the same thing. While working on wiring I left the key on. The Pertronix coil got hot enough to pop the top and leak oil everywhere. It also killed the unit under the cap. A call to Pertronix and they replaced the whole thing free. Excellent customer service.
@G-son I love it when someone comes in with the big science to shut down the doubters! T bucket harness, so no accessory switch on the key. Trying to iron out turn signals, but simple enough to disconnect the coil when keeping the key on.
Could bump the engine over until the points are open Sent from my iPhone using The H.A.M.B. mobile app
I've got no accessory switch on the '29 A Roadster but I went ahead and put a toggle switch hidden under the dash that kills power to the ignition and fuel pump for this reason as well as thinking it might be a theft deterrent. There has been a couple of times I haven't been able to steal my own car.
You COULD install a hidden anti theft on-off switch to kill power to the ign or coil like many do. That way you can stop the heating, plus have a small amount of anti-theft. That will keep you from having to rearrange your wiring. Sent from my SM-G981V using The H.A.M.B. mobile app
With a V8, at idle the ignition coil is "on" about 66% of the time. It's pretty easy to see why they will roast if the engine isn't running, it's basically a dead short. While a point type ignition it might only be 3 or 4 amps through the primary wiring when running it will get really toasty.
The diffrence is not just that the current is switched off for a large part of the time with the engine running, it also takes time for it to rise from zero to max each time it is switched on. So the actual current and power going into an ignition coil is VERY different when you compare a running engine and a constant flow of current.